One of my favourite lesson package to carry out for lesson on density is “Gold Ingot Scam”. It’s in the form of a case study in which students role-play as police officers. This is based on a real crime in Singapore in 2011.

I like this activity because there are videos from Crimewatch that can be used for pre and post lesson. In fact, in the part 2 of the video, it shows the detective carrying out the experiment.

I did this as a group work with my students.

Each group receive an electronic balance, a pendulum bob wrapped with Ferero Roche gold foil and a measuring cylinder.

The pendulum bob is kinda tricky though. The small one will not show much increase in water level, but the medium bob might get stuck in the cylinder. They kinda vary slightly in size, so you have to check beforehand. I was blessed with a lab tech who was willing to check that the medium bobs used did not get stuck in the cylinder. Luckily it was only 10 sets needed for him to check *phew*

I provided for the students a mock police report and a template for them to complete their report.

I did not provide instructions as I wanted the students to figure out on their own. Most generally got it that they have to measure mass and volume. But, while they’re were carrying out the experiment, I did spot some mistakes though.. such as

Measuring volume, then mass (with water droplets still on sample!!)

Not releasing the sample completely in the measuring cylinder. Some held on to the string, with the sample in the middle of the cylinder filled with water.

In the next lesson, I discussed these with them and elicit response from them on how those steps can affect the results.

For those keen for the lesson materials, you can get the materials here.

Add a pieces few leaves of red cabbage into a beaker of hot water. The leaves will decolourise and the solution will eventually turn purple. We will use this solution as the indicator. Add 2 drops into different samples and observe for colour change.

You can encourage students’ participation by allowing them to bring their own samples. Students generally are more excited to work on stuff that they contributed.

You can also extend this activity by giving them time to make their own indicator paper which they can bring home. Simply cut strips of filter paper, soak it in red cabbage juice and let it air dry. Students can then use them by dipping it into samples.